A prior-art vehicle suspension system that absorbs shocks adaptively in response to changing conditions is known, for example, from "ESAC--Electronically Controlled Traveling Gear Shock Absorption," which is WABCO Publication 826 001 173 3/8.94 published by WABCO Westinghouse Vehicle Brakes, WABCO Standard GmbH.
The prior-art ESAC suspension system selects a shock-absorption characteristic (soft, medium, or hard) that is most suitable for the current driving condition. In undisturbed travel, for example, the system provides soft, purely comfort-oriented shock absorption. If the vehicle should veer in response to a sudden steering action, on the other hand, the system switches to harder, and therefore safer, shock absorption. Shock absorption also hardens when unevenness in the road surface causes excessive deflections in the suspension system. Adaptive variation of shock absorption is also especially helpful in reducing pitching motions in vehicles that have a short wheel base. During acceleration, the front-end of the bodies of such vehicles otherwise tend to rise up excessively while transferring weight onto the rear axle. During braking, the opposite motion occurs as the rear of the body rises and weight is transferred to the front axle.
The prior-art ESAC suspension system recognizes deflections in the suspension at three points. One sensor detects an average spring excursion at the front axle and two more sensors are placed at the left and right rear springs. These three points are sufficient to determine the plane of the body of the vehicle. The three spring excursions also determine what is called a body shock-absorption requirement.
As mentioned above, the shock absorbers are hardened in case of excessive motions of the body of the vehicle. In other words, the degree of uncoupling is reduced between the axles and body of the vehicle. In this condition, shocks pass from the axles through the suspension to the body with less filtering causing a reduction in comfort. Comfort is especially strongly impacted by small irregularities in the road surface when the suspension system has hardened in response to more gradual but larger hollows or mounds in the roadway.
It is therefore an object of the present invention to provide an improved adaptive suspension system that provides greater comfort, when possible, while maximizing travel safety even on poor roads.
It is another object of the present invention to improve the treatment of loaded goods in vehicles traveling on poor roads. Yet another object is to reduce the load on the shock-absorbers themselves as well as on their controls. A further object of the invention is to provide a software implementation that does not require costly additional hardware components.
It is another object of the present invention is to use a bad-road parameter that takes various effects into account without determining them in unnecessary and costly detail. Among these effects are under-damped axle oscillations. In principle, these oscillations could be determined from the high-frequency components of the output signals of sensors that measure deflection at the springs or piston speed at the shock absorbers. In practice, however, these high-frequency components are removed by filtering, and the effect of the under-damped axle oscillations is lost.
It is another object of the present invention to provide the maximum comfort compatible with travel safety by employing shock absorbers with continuously variable shock-absorption force.
It is also an object of the present invention to provide harder shock absorption on poor roads, even when the vehicle body does not experience excessive vertical motions. For example, short-wave unevenness in the road does not cause shock-absorber hardening in the prior-art system. By hardening the shock absorption in such cases, the present invention avoids an under-damped motion called "axle trampling," which is also a significant cause of road wear. Fluctuations in wheel load are also reduced, which improves the steering and propulsion characteristics of the tires, thereby further ensuring travel safety.